This study will compare the hypolipidemic effects and influence on cholesterol homeostasis of simvistatin at the current maximal approved dose (40 mg per day) with three higher doses (80 mg per day) in regular and time-release formulations and 160 mg per day in a time-release formulation in patients with primary hypercholesterolemia. After a four week dietary baseline patients will be assigned to one of these four preparations in a ratio of 1:3:3:3 for a period of 24 weeks. Efficacy, metabolic effects and safety will be evaluated on each dose regimen.